U.S. patent number 6,890,506 [Application Number 10/120,828] was granted by the patent office on 2005-05-10 for method of forming carbon fibers.
This patent grant is currently assigned to Penn State Research Foundation. Invention is credited to Peter C. Eklund, Avetik Harutyunyan, Bhabendra K. Pradhan.
United States Patent |
6,890,506 |
Harutyunyan , et
al. |
May 10, 2005 |
Method of forming carbon fibers
Abstract
Carbon fiber/tubes are prepared by pyrolyzing a catalyst system
that contains one or more diluents to facilitate control of the
diameter of the formed carbon fiber/tube.
Inventors: |
Harutyunyan; Avetik (Columbus,
OH), Pradhan; Bhabendra K. (State College, PA), Eklund;
Peter C. (Boalsburg, PA) |
Assignee: |
Penn State Research Foundation
(University Park, PA)
|
Family
ID: |
34555140 |
Appl.
No.: |
10/120,828 |
Filed: |
April 12, 2002 |
Current U.S.
Class: |
423/447.3;
423/445R; 423/447.1 |
Current CPC
Class: |
D01F
9/12 (20130101) |
Current International
Class: |
D01F
9/12 (20060101); D01F 009/12 () |
Field of
Search: |
;423/447.1,447.2,447.3,445R |
References Cited
[Referenced By]
U.S. Patent Documents
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Nanotubes: A Step Closer to Commercial Realization" Chemical
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1317-1318..
|
Primary Examiner: Hendrickson; Stuart L.
Assistant Examiner: Lish; Peter J
Attorney, Agent or Firm: McDermott Will & Emery LLP
Parent Case Text
RELATED APPLICATION
The present application claims priority to U.S. Provisional
Application Ser. No. 60/283,472 filed 12 Apr. 2001 and entitled
"METHOD FOR CONTROLLING THE DIAMETER OF CARBON NANOTUBES", the
entire disclosure of which is hereby incorporated in its entirety
herein by reference.
Claims
What is claimed is:
1. A method of forming a carbon fiber/tube, the method comprising:
providing a metalorganic, which contains a metal and a source of
carbon for incorporation into a carbon fiber/tube upon pyrolysis;
combining a diluent with the metalorganic to form a diluted
metalorganic, wherein the diluent comprises phthalocyanine or a
derivative thereof; and pyrolyzing the diluted metalorganic to form
the carbon fiber/tube.
2. The method according to claim 1, wherein the metalorganic is
subjected to a purification step prior to being combined with the
diluent.
3. The method according to claim 1, comprising isolating the formed
carbon fiber/tube.
4. The method according to claim 1, wherein the metal comprises
iron, nickel or cobalt.
5. The method according to claim 1, comprising pyrolyzing the
diluted metalorganic at a temperature from about 100.degree. C. to
about 1000.degree. C.
6. The method according to claim 1, comprising forming a carbon
fiber/tube having a cross-section of less than one micron.
7. The method according to claim 1 further comprising: controlling
the diameter of the carbon fiber/tube by adjusting the amount of
diluent added to the metalorganic.
8. The method according to claim 7, comprising reducing the
diameter of the formed carbon fiber/tube by increasing the amount
of diluent.
9. The method according to claim 7, comprising isolating the formed
carbon fiber/tube.
10. The method according to claim 7, comprising pyrolyzing the
diluted metalorganic at a temperature from about 100.degree. C. to
about 1000.degree. C.
11. The method according to claim 7, wherein the formed carbon
fiber/tube has a cross-section of less than one micron.
12. A method of controlling the diameter of a carbon fiber/tube,
the method comprising: diluting a catalyst of formula (M.sub.1 Pc)
with a diluent comprising phthalocyanine or a derivative thereof,
where M.sub.1 is a metal and Pc is a phthalocyanine or a derivative
thereof; and pyrolyzing the diluted catalyst to form a carbon
fiber/tube with a diameter corresponding to the concentration of
the metal in the diluted catalyst.
13. The method according to claim 12, comprising diluting the
catalyst by adding a non-metal diluent.
14. The method according to claim 12, comprising diluting the
catalyst with a non-catalytic metal diluent.
15. The method according to claim 12, wherein M.sub.1 is nickel,
iron, or cobalt.
16. The method according to claim 15, comprising diluting the
nickel, iron or cobalt based catalyst by adding a metal free
phthalocyanine to the metal catalyst.
17. The method according to claim 12, comprising purifying the
diluted catalyst prior to pyrolysis.
18. The method according to claim 12, comprising separating the
formed carbon fiber/tube from the catalyst.
19. The method according to claim 12, comprising pyrolyzing the
diluted catalyst at a temperature from about 100.degree. C. to
about 1000.degree. C.
20. The method according to claim 12, comprising forming a carbon
fiber/tube having a cross-section of less than one micron.
Description
FIELD OF THE INVENTION
The present invention relates to a method for the production of
elongated carbonaceous articles, such as carbon fibers and
nanotubes. The present invention has particular applicability in
manufacturing carbon nanotubes having variously sized
diameters.
BACKGROUND
Carbon-based materials, in general, enjoy wide utility due to their
unique physical and chemical properties. Recent attention has
turned to the use of elongated carbon-based structures, such as
carbon filaments, carbon tubes, and in particular nanosized carbon
structures. It has been shown that these new structures impart high
strength, low weight, stability, flexibility, good heat
conductance, and a large surface area for a variety of
applications.
Of growing commercial interest is the use of single-wall carbon
nanotubes to store hydrogen gas, especially for hydrogen-powered
fuel cells. Other applications for carbon fiber/tubes materials
include catalyst supports, materials for manufacturing devices,
such as a tip for scanning electron microscopes, electron field
emitters, capacitors, membranes for filtration devices as well as
materials for batteries.
The formation of carbon filaments through catalytic decomposition
of hydrocarbons is known. For example, U.S. Pat. No. 5,165,909 to
Tennent et al., disclose the production of carbon fibrils
characterized by a substantially constant diameter and a length
greater than about 5 times the diameter by continuously contacting
metal particles with a gaseous, carbon-containing compound to
catalytically grow the fibrils. European Patent 56,004B1 to Yates
et al. discloses methods of preparing iron oxides for the
production of carbon filaments. U.S. Pat. No. 5,780,101 to Nolan et
al. discloses methods of producing highly crystalline nanotubes by
the catalytic disproportionation of carbon monoxide in the
substantial absence of hydrogen.
U.S. Pat. Nos. 5,872,422 and 5,973,444 both to Xu et al. disclose
carbon fiber-based field emission devices, where carbon fiber
emitters are grown and retained on a catalytic metal film as part
of the device. Xu et al. disclose that the fibers forming part of
the device may be grown in the presence of a magnetic or electric
field, as the fields assist in growing straighter fibers.
Additional conventional synthesis methods for carbon nanotubes
include carbon arc discharge (S. Iijima, Nature, 354, 56, 1991) and
catalytic pyrolysis of hydrocarbon (M. Endo, K. Takeuchi, S.
Igarashi, K. Kobori, M. Shiraishi, H. W. Kroto, J. Phys. Chem.
Solids, 54, 1841, 1993), which generate nanotubes often containing
traces of the catalyst particles used to generate them and
possessing highly variable dimensions. Synthesis of aligned
nanotube by pyrolysis of hydrocarbon with a patterned cobalt
catalyst on silica substrate was reported by M. Terrones et al,
Nature, 388, 52, 1997 and with iron nanoparticles in mesoporous
silica by W. Z. Li et al, Science, 274, 1701, 1996. The successful
production of carbon nanotubes in an alumina template by pyrolysis
of propylene has been disclosed by T. Kyotani, L. Tsai, A. Tomita,
Chem. Mater., 8, 2190, 1996.
Despite efforts in preparing carbon fiber/tubes, limited progress
has been realized in controlling the diameters of these materials,
particularly controlling the diameter of carbon nanotubes.
Accordingly, a need exists for the manufacture of carbon
fiber/tubes, in particular nanosized carbon-based fiber/tubes, with
improved control over the diameter of these materials.
BRIEF SUMMARY
An advantage of the present invention is a method of manufacturing
carbon fiber/tubes.
Additional advantages and other features of the present invention
will be set forth in the description which follows and in part will
be apparent to those having ordinary skill in the art upon
examination of the following or may be learned from the practice of
the present invention. The advantages of the present invention may
be realized and obtained as particularly pointed out in the
appended claims.
According to the present invention, the foregoing and other
advantages are achieved in part by a method of a manufacturing a
carbon article, e.g. a carbon fiber or nanotube. The method
comprises preparing a metal catalyst system having one or more
diluents; and pyrolyzing the metal catalyst system to form the
carbon fiber/tube. The diluents can be non-metal ligands, i.e.
metal-free organic compounds such as chelators.
Embodiments include preparing a metal catalyst system by adding a
non-metal diluent to a metal catalyst, e.g. adding a phthalocyanine
or derivative thereof to a nickel phthalocyanine metalorganic to
form the metal catalyst system, and pyrolyzing the metal catalyst
system from about 100.degree. C. to about 1000.degree. C.
Another aspect of the present invention includes a method of
controlling the diameter of a carbon fiber/tube. The method
comprises preparing a metal catalyst system by adding a diluent to
a metal catalyst; and pyrolyzing the metal catalyst system to form
a carbon fiber/tube with a diameter corresponding to the diluted
metal catalyst.
Additional advantages of the present invention will become readily
apparent to those skilled in this art from the following detailed
description wherein embodiments of the present invention are
described simply by way of illustrated of the best mode
contemplated for carrying out the present invention. As will be
realized, the present invention is capable of other and different
embodiments, and its several details are capable of modifications
in various obvious respects, all without departing from the present
invention. Accordingly, the drawings and description are to be
regarded as illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of the present invention will
become more apparent and facilitated by reference to the
accompanying drawings, submitted for purposes of illustration and
not to limit the scope of the invention, where the same numerals
represent like structure and wherein:
FIG. 1 illustrates a series of histograms showing the distribution
of the diameters of carbon fiber/tubes obtained by pyrolysis using
(a) a nickel phthalocyanine (NiPc) metalorganic, (b) a NiPc
metalorganic diluted with 75% of phthalocyanine; and (c) a NiPc
metalorganic diluted with 92% of phthalocyanine.
FIG. 2 is a chart showing the relationship between the average
diameter of carbon nanotubes to the degree of dilution of the
catalyst from which the carbon nanotubes were produced.
DESCRIPTION OF THE INVENTION
The present invention contemplates a new technique of forming
carbon-based structures, e.g. carbon fiber/tubes, with a certain
degree of control over the diameter of the formed carbon structure.
The carbon articles manufactured in accordance with the present
invention can take any elongated form, such as that of a
fiber/tube, fibril, filament etc. It is understood that the terms
"carbon filaments", "carbon whiskers", "carbon fibers", and "carbon
fibrils", are sometimes used interchangeably by those in the art,
all of which however, are herein contemplated by the present
invention. The elongated forms can be of any morphology, such as
straight, branched, twisted, spiral, helical, coiled, ribbon-like,
etc. and have a length of a few nanometers (nm) to several hundred
microns.
The inner core of these articles can be solid, hollow or can
contain carbon atoms that are less ordered than the ordered carbon
atoms of the outer region. The carbon article of the present
invention can be in the form of a tube, and in the size of a carbon
nanostructure such as those selected from nanotubes, single-walled
nanotubes, hollow fibrils, nanoshells, etc. The nanostructures used
in the present invention can have a cross-section or diameter of
less than 1 micron, e.g. from about 0.1 nm to less than 1,000 nm,
e.g., from about several nanometers to about 500 nm. In en
embodiment of the present invention the cross-section of a
nanostructured carbon article is from about 20 nm to about 200
nm.
In part, the type of carbon article formed depends on the type and
nature of the catalyst used in the process. For example a nanosized
catalyst, i.e. a catalyst having a displacement of less than one
micron, can form a nanosized structure. Carbon articles can be
formed by pyrolysis of a carbon source in the presence of a
catalyst. In an embodiment of the present invention, the carbon
source is a component of the catalyst system. For example, carbon
nanotubes can be made by pyrolysis of a metalorganic compound, such
as a nickel phthalocyanine (NiPc), where the organic component of
the metalorganic compound provides the source of carbon used to
generate the carbon structure. This method advantageously permits
the preparation of well-aligned carbon fiber/tubes over large areas
and on different substrates.
Through experimentation and investigation, it was discovered that
by diluting the catalyst, i.e. adding additional components to a
catalyst comprising at least one metal, the diameter of the
resulting carbon structure formed from the diluted catalyst can be
reduced. It is believed that the addition of components to the
catalyst results in an increased distance between metal atoms in
the composition, i.e. there is a decreased concentration of metal
atoms per unit volume. Pyrolysis thereafter results in smaller
metal clusters. Since carbon fiber/tubes are believed to be grown
from the metal clusters, decreasing their size, in turn, results in
smaller diameters of the formed carbon fiber/tubes. Hence, dilution
provides a systematic method of controlling the diameter size of
carbon structures formed therefrom.
In accordance with the present invention, the catalyst should be
capable of being diluted by the addition of one or more components
or their equivalents. Suitable catalysts include, for example,
transition metal-based catalyst, such as chromium, molybdenum,
iron, nickel, cobalt, etc. and alloys thereof. In one aspect of the
present invention, the catalyst comprises an iron, nickel or cobalt
metal with one or more ligands, such as a phthalocyanine (Pc)
(C.sub.32 H.sub.16 N.sub.g) or a derivative thereof, e.g. (C.sub.32
H.sub.16 N.sub.8 R.sub.x) where R is an alkyl or ether or ester,
etc. as is known in the arts and "x" is the number of times R
occurs in the compound as is also known in the art. It is also
contemplated that the R substituent can differ at different
locations on the ligand. In this case, the metal can be diluted
with additional ligands, i.e. a metal free diluent, such as the
addition of Pc to a nickel catalyst. In one aspect of the present
invention, the diluents are chelators that are commonly used as
ligands in metal complexes. These catalysts can be prepared by
conventional techniques as known in the art.
The catalyst can be deposited on chemically compatible supports.
Such supports should not poison the catalyst, should be easily
separated if necessary from the carbon products after they are
formed. In an embodiment of the present invention, the catalyst is
supported on a chemically compatible porous substrate, such as a
refractory support. Alumina, carbon, quartz, silicates, and
aluminum silicates such as mullite may be suitable support
materials.
In practicing an embodiment of the present invention, carbon
articles can be formed in a chamber containing an inert and/or
reducing gas by heating the diluted catalyst at elevated
temperatures for an effective amount of time. By an effective
amount of time, it is meant the amount of time needed to produce
the desired elongated structure. This amount of time will generally
be from about several seconds to as long as several days depending
upon the diluent, catalyst, and desired article. Heating the
diluted catalyst at sufficient temperatures causes it to decompose
and causes carbon deposits to form on the metal components in the
catalyst. Continued heating causes the continued deposition of
carbon and the growth of an elongated article.
The reaction temperature should be high enough to cause the
catalyst to form carbon materials. The precise temperature limits
will depend on the specific catalyst system used. In an embodiment
of the present invention, the chamber is maintained at a
temperature from the decomposition temperature of the
carbon-containing compound to the deactivation temperature of the
catalyst. Generally, this temperature will range from about
100.degree. C. to about 1000.degree. C., and preferably from about
500.degree. C. to about 850.degree. C.
EXAMPLE
An example of forming a carbon nanotube with various sized
diameters was undertaken. In this example, NiPc was prepared with
metal-free Pc (H.sub.2 Pc) and used as both a catalyst and a carbon
source at the same time. As a further example of metal diluents,
the present invention also contemplates catalyst systems that are
diluted by the addition of metal diluents. For example, composition
having (M.sub.1 Pc).sub.x (M.sub.2 Pc).sub.1-x where M.sub.1 and
M.sub.2 are different metals are also contemplated.
In this example, phthalocyanines were purified by twice subliming
the sample at about 480.degree. C. under vacuum. This produces
predominately the beta form of MPc (where M is a metal), the more
stable of its polymorphic forms. Diluted catalyst systems were
prepared by subliming a predetermined mixture of NiPc with H.sub.2
Pc powders in a desired proportion to yield (NiPc).sub.x (H.sub.2
Pc).sub.1-x. Three different catalysts were prepared where x is 1,
0.25 and 0.08 by this method.
Carbon nanotubes were then formed by pyrolyzing the catalyst
systems. Pyrolysis was carried out under a atmosphere of argon and
hydrogen (1:1 v/v) at a flow of about 40 cc/min in a quartz flow
reactor. This particular reactor comprised a two-zone electrical
furnace with independent temperature control for each zone. A
quartz substrate was placed in the reactor which was previously
cleaned by sonication in ethanol prior to pyrolysis. The source
material was then placed in the first zone for vaporization.
Initially, the first zone was heated to about 480-520.degree. C.,
while the second zone was heated to about 800-920.degree. C. After
about 10-20 minutes, the temperature of the first zone was
increased to that of the second zone and temperature was maintained
for an additional 15-30 minutes. The reactor was then cooled to
room temperature under an argon atmosphere. The carbon deposit was
then separated from the substrate. The carbon deposit could be
separated by scrapping which resulted in a powder or by immersing
the substrate into an hydrofluoric acid bath which resulted in a
film of the material.
After isolating the carbon mass, characterization thereof showed
that the diameter of the formed carbon fiber/tubes depended on the
degree of dilution of the metal in the catalyst system. For
example, carbon nanotube diameters grown by pyrolysis of (a) NiPc;
(b) (NiPc).sub.0.25 (H.sub.2 Pc).sub.0.75 ; and (c) (NiPc).sub.0.08
(H.sub.2 Pc).sub.0.92 showed a progressive decrease in the
size.
FIGS. 1a-c illustrate histograms of nanotube diameter distributions
estimated from high resolution scanning electron micrographs for
grown from the pyrolysis of catalyst systems (a), (b) and (c). As
illustrated in FIGS. 1b-c, the higher dilution, the lower the
diameter of the formed carbon nanotube. The decrease in diameters
is further illustrated by the chart in FIG. 2 which plots the
approximate correlation between "x" the amount of dilution for this
particular system and the corresponding diameter of the formed
carbon nanotube.
Although the present example has been described where the carbon
source is a component of the catalyst system, additional external
carbon sources can be added. For example, a carbon containing
precursor, e.g. a C.sub.1-18 hydrocarbon, can be introduced to the
chamber and in contact with the catalyst with the application of
heat. This can occur before, during and/or after pyrolysis of the
catalyst system. Also additional materials and/or conditions can be
included to optimize this system without departing from the scope
or spirit of the present invention.
The present invention enjoys industrial applicability in
manufacturing various types of carbon structures, particularly
carbon nanotubes with a degree of control over the diameter of the
nanotube. In the preceding detailed description, the present
invention is described with reference to specifically exemplary
embodiments thereof. It will, however, be evident that various
modifications and changes may be made thereto without departing
from the broader spirit and scope of the present invention, as set
forth in the claims. The specification and drawings are,
accordingly, to be regarded as illustrative and not restrictive. It
is understood that the present invention is capable of using
various other combinations and environments and is capable of
changes or modifications within the scope of the inventive concept
as expressed herein.
* * * * *